This invention relates to improvements in a speed-changing hydraulic pressure control system for a belt-type continuously variable transmission, by which hydraulic for speed-changing of the belt-type continuously variable transmission is effectively controlled without occurring slip of a belt.
A variety of speed-changing hydraulic pressure control systems for a belt-type continuously variable transmission have been proposed. One of them will be briefly discussed with reference to FIG. 6 and includes a pressure regulating valve 230 which is supplied with a hydraulic pressure supplied from a line pressure supply valve 200 and a hydraulic pressure (signal pressure) supplied from an electrically controlled hydraulic pressure control valve 210. The line pressure supply valve 200 is adapted to supply the regulated hydraulic pressure. Additionally, the pressure regulating valve 230 is hydraulically connected to a forward clutch 220. When the signal pressure is output from the electronically controlled hydraulic pressure control valve 210, an engaging pressure of the forward clutch 220 is regulated in a manner to balance with a resultant force of the biasing force of a return spring 232 of the pressure regulating valve 230 and the signal pressure, as shown in FIG. 6. Here, the output pressure of the pressure regulating valve 230 increases in proportion to an increase of the output pressure of the electronically controlled hydraulic pressure control valve 210.